Real time bit rate switching for internet protocol television

ABSTRACT

A method, apparatus and computer program product are provided for delivering television programming to a subscriber. In one aspect the method includes receiving one or more channels of program content, and encoding each channel a plurality of times, each time at a different rate producing multiple rate encoded signals for each channel. The method can further include transmitting the multiple rate encoded signals to a central office over a network, determining an available bandwidth of a downstream link to a subscriber and a current bit rate available for transmission to the subscriber. The method can further include selecting a best available bit rate from the multiple rate encoded signals for a requested channel and transmitting the selected rate encoded signal to the subscriber.

BACKGROUND

The following disclosure relates to network communication.

Delivery of broadcast television signals has advanced over the yearsfrom classical over-air delivery channels to cable, satellite, andtelephone delivery systems. As the delivery mechanisms have changed, sohave the challenges in delivering the content efficiently to theconsumers. Delivery of the content is constrained by resources of thedelivery systems including bandwidth limitations of the communicationchannels used. As content has expanded to include pay-per-view services,digital music and a myriad of new channel offerings, the challenges tothe delivery systems to provide such content efficiently have grown.Relatively recently, additional system level pressure has been added dueto the demand from the consumer for higher quality content delivery(e.g., high definition television, HDTV).

Most delivery systems have inherent bandwidth limitations that limit theamount of content that can be delivered. The bandwidth limitations canbe resource dependent or channel dependent, in that limitations mayexist in each end of the delivery system at a transmit or receive side(e.g., finite amount of data that is able to be transmitted or receivedby the transmitting or receiving devices), or in the communicationchannel itself (e.g., bandwidth at a given frequency for broadcast, ordownlink bandwidth provided in a digital subscriber line (DSL) system).

In the last 10 years, the existing telephone company infrastructuresystem (hereinafter the“Telco System”) has been utilized to delivercontent to users. DSL systems have been made available to provide highspeed internet access to consumers. The Telco System has inherentbandwidth limitations in the amount of data that can be delivered overthe copper paths prevalent in the system. These limitations have limitedthe effectiveness of using the Telco System to deliver high bandwidthcontent over the existing system. With the advent of advanced codectechnology, the Telco System is now a viable delivery system forstandard definition and high definition video and audio services. As apractical matter, other delivery systems (satellite for example) are notas constrained in terms of bandwidth. Further consumer applications thatnecessitate even more bandwidth, for example watching and recordingdifferent channels, have made the Telco System less desirable overall asa delivery mechanism.

SUMMARY

In one aspect, a method is provided for delivering televisionprogramming to a subscriber that includes receiving one or more channelsof program content, and encoding each channel a plurality of times, eachtime at a different rate producing multiple rate encoded signals foreach channel. The method further includes transmitting the multiple rateencoded signals to a central office over a network, determining anavailable bandwidth of a downstream link to a subscriber and a currentbit rate available for transmission to the subscriber. The methodfurther includes selecting a best available bit rate from the multiplerate encoded signals for a requested channel and transmitting theselected rate encoded signal to the subscriber.

Aspects of the invention can include one or more of the followingfeatures. The step of determining a current bit rate available fortransmission to the subscriber can include determining one or moreadditional signals that are to be transmitted to the subscriber and acombination of best available rate encoded signals for the one or moreadditional signals and the requested channel and combining the bestavailable rate encoded signals in a stream for output to the subscriber.The step of encoding can include encoding each channel three times, atrespective high, medium and low bit rates. The step of encoding caninclude encoding each channel at rates selected from the group ofsubstantially 1.5 Mbps, 2 Mbps, 4 Mbps, 6 Mbps, 8.5 Mbps, and 12 Mbps.The step of transmitting the rate encoded signals to a central officecan include streaming the rate encoded signals over an IP network wherestreaming can include multicasting the rate encoded signals for eachchannel to a plurality of central offices. The step of streaming caninclude streaming the rate encoded signals on a different IP multicastaddress.

In another implementation a method is provided for delivering televisionprogramming to a subscriber that includes receiving one or more channelsof program content, encode each channel a plurality of times, each timeat a different rate producing a multiple rate encoded signals for eachchannel and transmit the multiple rate encoded signals to a centraloffice over a network for distribution to individual subscribers.

In another implementation, a method is provided for deliveringtelevision programming to a subscriber including receiving one or morechannels of program content, each channel encoded at a plurality ofdifferent rates thereby providing multiple rate encoded signals,determining an available bandwidth of a downstream link to a subscriberand a current bit rate available for transmission to the subscriber,selecting a best available bit rate from the multiple rate encodedsignals for a requested channel and transmitting the selected rateencoded signal to the subscriber.

In another implementation, an apparatus is provided that includes atermination device including an input interface for receiving one ormore channels of program content, each channel encoded at a plurality ofdifferent rates thereby providing multiple rate encoded signals, abuffer to buffer the multiple rate encoded signals and a bite rateengine. The bit rate engine is operable to determine an availablebandwidth of a downstream link to a subscriber, determine a current bitrate available for transmission to the subscriber, and select a bestavailable bit rate from the multiple rate encoded signals for arequested channel. The apparatus includes a multiplexer operable tocombine selected signals for the subscriber and an output interface fortransmitting the combined signal to the subscriber.

Aspects of the invention can include one or more of the followingfeatures. The apparatus can include a rule set including priority rulesfor use in determining a best available bit rate from the multiple bitrate encoded signals. The apparatus can include a user bit rate usagedatabase including data indicating a current bit available fortransmission to the subscriber.

Implementations can include one or more of the following advantages. Adelivery system is provided for offering Telco operators an ability touse there existing, advanced network to offer high quality video andaudio services in an optimal manner without compromising their inherentbandwidth constraints. The delivery system provided maximizes thebandwidth available to the consumer (e.g., to the home) based upon thebit rates consumed by each television subscriber in the consumerenvironment. Unlike a conventional broadcast system that broadcasts allchannels at a consistent rate, the delivery system proposed willselectively deliver different rate content to the consumer. In theproposed delivery system, a central distribution location will broadcastcontent at a plurality of fixed rates to local central officedistribution centers. The central office distribution centers areresponsible for understanding specific consumer need, and selectivelytransmitting particular rate content to the individual consumer, and inone implementation, at a highest bit rate based on available bandwidthto the consumer.

In the proposed delivery system, the end subscriber will be able to viewat any point in time the highest quality channel of data based upontheir current bit rate capacity. In one implementation it was found thatstatistically, approximately 80% of the subscribers to the deliverysystem will be viewing the best quality channel available all of thetime, the quality level being comparable to or better than conventionalsatellite and cable delivery systems.

The details of one or more embodiments of the invention are set forth inthe accompanying drawings and the description below. Other features,objects, and advantages of the invention will be apparent from thedescription and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a content delivery system.

FIG. 2 is a block diagram of a rate component of the delivery system.

FIG. 3 is a flow diagram of a method for delivering content to asubscriber.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

FIG. 1 shows a content delivery system 100 in which multiple encoderssets 110(1)-110(n) are connected to video/audio (video, audio, or both)sources 120. Each encoder set 110 includes one or more individualencoders 112(1)-112(n).

Encoders 112(1)-112(n) can be, for example, audio or video encoders thatreceive and encode input signals 105(1)-105(n) for transmission.Received content (which is subsequently encoded for delivery) can be ofthe form of television signals representing broadcast channels (e.g.,standard or high definition), channel guides, live broadcast feeds, orother content. Encoders 112(1)-112(n) can support various encodingprotocols including MPEG-2, H264 and VC-1 codec standards. Encoders112(1)-112(n) typically can encode and transmit data at multiplebitrates. The bitrate an encoder uses to encode a signal can be variedbased on, for example, the complexity of the signal, the availablebandwidth in an output channel, or the quality desired or required forthe encoded signal. In one implementation, each encoder 112 in a set ofencoders 110 encodes the same video/audio/data content at a differentconstant (or capped) bit rate. For example, in one implementation eachencoder set 110 includes three encoders 112 encoding a same receivedinput signal 105 at rates set at 1.5 Mbps (megabits per second), 2.5Mbps, and 4.0 Mbps for use, for example, with standard definitiontelevision signals. For high definition television signals, other bitrate combinations can be used (e.g., 6 Mbps, 8.5 Mbps and 12 Mbps).Other encoding rates can be selected and other numbers of encoders 112can be included in each encoder set 110. The purpose for the duplicativecontent encoding will be discussed in greater detail below.

Each encoder 112 receives an input signal 105 (e.g., uncompressed analogor digital audio, video, or data), encodes the input signal 105 using anencoding unit (not shown), and transmits an encoded data message using atransmitter (not shown). The data message can be encoded with a fixed orvariable bitrate and can be, for example, a stream of data or a seriesof discrete packets of data.

As discussed above, plural encoders 112 can be included in each encoderset 110. In one implementation, the bit rates selected for each encoderand combination of bit rates available for a given channel can bedetermined based on a number of criteria including a content provider'srequirement for minimal bit rate, business needs of a service provider,network capability of the service provider and/or other criteria. Thesecriteria may lead a service provider (i.e., the entity providing thedelivery system) to define different combinations of bit rate optionsper channel as well as different numbers of bit rate optional channels.In the implementation described above, plural encoders 112 arecontemplated for each channel. Optionally, only a single encoder may beused. Additionally, it should be noted that an encoder set can encodethe same channel multiple times on the same physical platform or onseparate platforms.

Encoders 112(1)-112(n) transmit encoded data over one or more networks120(1)-120(n) (only one is shown) to one or more central offices150(1)-150(n) (again, for the purposes of clarity, only one is shown).In one implementation, each encoder 112(1)-112(n) streams an individualencoded signal over a different internet protocol IP multicastdestination address. In this implementation, destination addresses areassociated with a given central office 150, so that multiple copies(encoded at different rates) of the audio/video content are delivered toa given central office 150 location. As one of ordinary skill in the artwould recognize, streaming to multiple destination addresses (i.e.,multicast) is one means of accomplishing the delivery of the encodedcontent to multiple destinations. Other means including subscriptiondelivery protocols or systems can be used.

Networks 120(1)-120(n) can be internet protocol (IP) networks, otherpacket switched communication networks or other communication networks.In the content delivery system 100 shown, each encoder 112 communicateswith an Ethernet switch 125 that acts as a gateway to a distributionbackbone 127 of a network (e.g., distribution backbone of a TelcoSystem) that in turn is coupled to one or more central offices 150. Inthe implementation shown, redundant switches 125(1) and 125(2) are usedto ensure fault tolerant delivery. Alternatively, other communicationnetworks including wide area networks, local area networks, public andprivate networks or combinations of these can be used to deliver therate encoded data to the central office(s) 150. In otherimplementations, each encoder may communicate with a multiplexer that isused to combine the encoded data streams into a single output stream,which can be a constant bit rate stream. The single output stream canthen be delivered to the respective destination. A demultiplexer can beincluded at each destination that is used to separate the individualstreams for further processing (e.g., distribution to individualsubscribers).

Central office 150 includes one or more termination units. In theimplementation shown, central office 150 includes two digital subscriberline access multiplexers (DSLAMs) 160 and a rate component 170). In theimplementation shown, a redundant set of DSLAMs 160 and rate components170 are provided at a central office 150.

DSLAM 160 is a network device at central office 150 that receivessignals from multiple customer Digital Subscriber Line (DSL) connectionsand puts the signals on a high-speed backbone line (e.g., backbone 127)using multiplexing techniques. In the implementation shown, a DSLAMprovides termination (i.e., acts as a termination device) at the centraloffice. Other forms of termination devices are possible includingoptical line termination devices (e.g., for a passive optical network),cable modem termination devices, and the like.

Rate component 170 is operable to identify usage of a specificsubscriber (e.g., customer 180) with respect to bit rate consumption andfor transmitting (via the termination device) the encoded channel(s) tosubscribers based on a current availability of bandwidth. As discussedabove, typically the link between the central office 150 and thesubscriber has a capacity limit, such limit supporting all of thedemands for content in a given subscriber environment. For example, asubscriber may have multiple television sets, including one or moretuners (or virtual tuners, e.g., each being associated with adestination IP address), each of which may be operated and produce arequest for content to be delivered from the central office 150. Therate component 170 manages demand (e.g., the numbers of tunersrequesting content) and allocated bandwidth (e.g., the subscriberdownlink bandwidth) and controls the selection and transmission ofencoded channels to a given subscriber. In one implementation, ratecomponent 170 will transmit a highest bit rate encoded channel available(assuming bandwidth to the subscriber is available). As bandwidth isconsumed, for example to support multiple demands from a givensubscriber, lower bit rate options may be selected for transmission.Rate component 170 manages the transitions between the selection of thevarious rate encoded signals of the same channel, in one implementation,in real-time. The details of the selection process used by the ratecomponent 170 are discussed in more detail below. In the implementationshown, rate component 170 is in line with, and separate from, thetermination device (e.g., DSLAM 160). In one implementation, ratecomponent 170 (including hardware, software, engines, processes,firmware or combinations thereof) or portions thereof are included inthe termination device.

Central office 150 is coupled to a plurality of customers 180 by anetwork 175.

Network 175 can be of the form of a packet switched communicationnetwork that transfers IP packets addressed accordingly to a givensubscriber. Network 175 can be wired (including wire or opticaltransmission paths), wireless or a combination of both. Network 175 canbe a local area network, a wide area network, public network, privatenetwork or combinations of these. In the specific example shown, network175 is provided using a conventional Telco system including loop andaggregation technology as required. Other network connections, i.e., nonIP, are possible.

Customer 180 includes a receiver, such as set top box 190. Set top box190 can include a demultiplexer (not shown) for demultiplexing thereceived rate encoded signals into channels and one or more decoders192(1)-192(n) for decoding the rate encoded signal channels receivedfrom the central office 150. In one implementation, the receiverincludes a variable bit rate decoder that is capable of decoding thevarious different bit rate signals that are delivered from the centraloffice. Alternatively, plural decoders can be used to decode thedifferent encoded bit rate signals.

FIG. 2 shows an block diagram of rate component 170 of FIG. 1. Ratecomponent 170 includes an input interface 210, buffer 220, bit rateengine 230, multiplexer 240 and output interface 250.

Input interface 210 is a module that is operable to receive the multipleinput channels over network 120. In one implementation, input interfaceis an IP input interface for receiving IP packets from an IP network. Inthe simplified implementation shown in FIG. 2, input interface 210receives three encoded signals associated with a single source includinga low, medium and high bit rate input signal. In this example, Channel A(Low Bit Rate) refers to an incoming channel from the central officethat has been encoded at a low bit rate, also known as aggressive bitrate. Channel A (Med Bit Rate) refers to the incoming channel from thecentral office that is encoded at a medium bit rate, also known asaverage bit rate. Channel A (High Bit Rate) refers to the incomingchannel from the central office that is encoded at a high bit rate, alsoknown as non-aggressive bit rate. As discussed above, other numbers ofinput sources and other numbers and levels of rates can be used.

Buffer 220 is operable to for caching data received. In oneimplementation, buffer 220 caches a group of pictures, also known as aGOP of a given channel (e.g., of Channel A), and other channels on thenetwork. Buffer 220 can be of the form of a circular buffer thatoperates to overwrite data on roll over. Depending on a decision made bybit rate engine 230, a portion of the data stored in the buffer 220 canbe directed to the output of the rate component 170.

Bit rate engine 230 is operable to decide which bit rate of a requestedchannel to transmit to the output. The decision can be based upon thecurrent use of the available downlink bandwidth (i.e., the bit ratesused for signals currently being transmitted to an nd subscriber's home)taking into account the subscriber's current usage and total availablebandwidth (i.e., stored in a user bit rate usage database 234), as wellas pre-defined business rules which are stored in a rule set 232associated with the bit rate engine 230. The output of the bit rateengine 230 is a selected bit rate of a requested channel (e.g., ChannelA). Once a decision is made, a selected source stream can be requestedfrom the buffer 220 and passed to the multiplexer 240. Details ofselection are discussed below.

Multiplexer 240 is operable to multiplex selected data (e.g., selectedchannels of data, each channel at a selected bit rate based decisions ofthe bit rate engine 230). In one implementation, multiplexer 240multiplexes the output of the bit rate engine 230 with other streams.More specifically, multiplexer 240 is used to combine the selectedencoded data streams (e.g., a selected Channel A stream, a selectedChannel B stream, etc.) into a single output stream, which can be aconstant bit rate stream. The single output stream can then be deliveredto the respective destination, i.e., the subscriber. A demultiplexer canbe included at each destination that is used to separate the individualstreams for further processing (e.g., distribution to individualsubscriber tuners).

Output interface 250 is operable to process the output stream from themultiplexer to facilitate transmission to the subscriber. In oneimplementation, output interface 250 is an IP output interface and isoperable to encapsulate (e.g., package) the received output stream fromthe multiplexer 240 into an IP format and transmit the IP packetsdownstream (e.g., using DSLAM 160) over an IP network to the subscriber.

Referring now to FIG. 3, a method is described for use by the bit rateengine 230 in deciding which input stream to select for downstreamtransmission. A determination is made as to the level of the currentavailable bandwidth (e.g., bit rate usage) per subscriber (310).Subscriber refers generally here, and throughout this document, as asingle point of delivery of data from the central office. The subscribermay have plural devices (e.g., tuners) that are to receive the data anddisplay/play/interact with the content. In one implementation, asubscriber has a plurality of tuners (or virtual tuners associated withan IP address) that request and receive specific data (e.g., atelevision channel delivered at a particular bit rate). Each tuner maybe associated with a receiver which receives the data stream from thecentral office. Alternatively, each tuner may itself include a receiver.In one implementation the available bandwidth per subscriber is fixed.Alternatively, the available bandwidth per subscriber or for aindividual subscriber can vary or be dynamically or otherwise adjusted.For purposes of clarity, only a fixed allocation system is discussedbelow.

Once the available bandwidth is determined, and based upon the currentavailable bandwidth per subscriber, a decision is made which sourcechannel to select (e.g., which of the different bit rate encodedversions of the same source channel) 320. In one implementation, therate component 170 offers/provides the source channel with the highestbit rate that does not exceed the overall bit rate available persubscriber. As an example, if a subscriber has access to 10 Mbps, andcurrently 3 Mbps are in use (due to other previous selections), when achannel is requested, the bit rate engine will select the channel withthe highest bit rate that does not exceed the available bit rate (e.g.,7 Mbps).

Thereafter, the selected channel and previously selected data arecombined 330 (e.g., by multiplexer 240) and delivered 340 (e.g., throughthe termination device) to the subscriber. In one implementation, thedecision as to what rate data is delivered is a dynamic, in that theavailable bandwidth can change over the course of time (in either fixedor dynamic allocation implementations). As the available bandwidthchanges or in conjunction with periodic or otherwise checks, thedecision process as to what rate data is delivered to a subscriber canbe re-assessed, resulting in a different rate selection, andnecessarily, delivery of different rate data to the subscriber. In theexample given above with a 10 Mbps subscriber maximum rate, at asubsequent time, the subscriber may cancel or otherwise designate thatthe initial 3 Mbps, data is no longer required. At this time, adetermination can be made as to whether higher rate data is available todeliver based on previous requests (e.g., previously 6k Mbps data mayhave been selected, where 8 Mbps was available due to the 7 Mbpsavailable limitation, and once the available bandwidth limitation waslifted, the higher rate data can then be selected). If available, thehigher rate data can be delivered to the subscriber.

As one skilled in the art would recognize, as the total availablebandwidth to a given subscriber fills, conflicts may result requiringbit rate engine 230 to prioritize or otherwise decide what combinationof requested information is delivered. Ideally, the highest availablebit rate data is delivered to the subscriber. When bandwidth limitationsprevent the delivery of the highest rates, then one or more priorityschemes (e.g., embodied in rules stored in rule set 232) can be used todetermine an appropriate combination of rate data to deliver to thesubscriber. In one implementation, based on business reasons, operatorsmay decide to prioritize various services. Rule set 232 can include aconfiguration of business rules that define the priorities for conflictsituations. Examples of business rules that can be considered include:priority between high definition and standard definition channels;priority between various content, for example, channel A may have ahigher priority than channel B; priority between live broadcast channelsand on-demand channels; priority between a channel being recorded by theend user or viewed by the end user; and/or priority based on quality ofservice purchased by the end user. Other considerations can be applied.In one implementation, the bit rate engine offers the highest bit ratechannel based on the defined priorities that does not exceed the overallbandwidth available on the network.

A number of embodiments of the invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Theinvention of portions thereof can be implemented in hardware, software,firmware or the like and include discrete or integrated components.Though reference has been made to particular storage structures,termination devices, networks, network components, telephone networks,content and the like, the principals of the present invention areapplicable to other structures, devices, networks, content, componentsand the like. Nothing in this disclosure should be construed as limitingwith respect to the applicability of the invention to any particularhardware or other implementation.

Accordingly, other embodiments are within the scope of the followingclaims.

1. A method for delivering television programming to a subscribercomprising: Receiving one or more channels of program content; Encodingeach channel a plurality of times, each time at a different rateproducing multiple rate encoded signals for each channel; Transmittingthe multiple rate encoded signals to a central office over a network;Determining an available bandwidth of a downstream link to a subscriber;Determining a current bit rate available for transmission to thesubscriber; Selecting a best available bit rate from the multiple rateencoded signals for a requested channel; and Transmitting the selectedrate encoded signal to the subscriber.
 2. The method of claim 1 whereinthe step of determining a current bit rate available for transmission tothe subscriber includes: determining one or more additional signals thatare to be transmitted to the subscriber; determining a combination ofbest available rate encoded signals for the one or more additionalsignals and the requested channel; and combining the best available rateencoded signals in a stream for output to the subscriber.
 3. The methodof claim 1 wherein the step of encoding includes encoding each channelthree times, at respective high, medium and low bit rates.
 4. The methodof claim 3 wherein the step of encoding includes encoding each channelat rates selected from the group of substantially 1.5 Mbps, 2 Mbps, 4Mbps, 6 Mbps, 8.5 Mbps, and 12 Mbps.
 5. The method of claim 1 whereinthe step of transmitting the rate encoded signals to a central officeincludes streaming the rate encoded signals over an IP network.
 6. Themethod of claim 5 wherein the step of streaming includes multicastingthe rate encoded signals for each channel to a plurality of centraloffices.
 7. The method of claim 6 wherein the step of streaming includesstreaming the rate encoded signals on a different IP multicast address.8. A method for delivering television programming to a subscribercomprising; Receiving one or more channels of program content; Encodingeach channel a plurality of times, each time at a different rateproducing a multiple rate encoded signals for each channel; andTransmitting the multiple rate encoded signals to a central office overa network for distribution to individual subscribers.
 9. The method ofclaim 8 wherein the step of encoding includes encoding each channelthree times, at respective high, medium and low bit rates.
 10. Themethod of claim 9 wherein the step of encoding includes encoding eachchannel at rates selected from the group of substantially 1.5 Mbps, 2Mbps, 4 Mbps, 6 Mbps, 8.5 Mbps and 12 Mbps.
 11. The method of claim 8wherein the step of transmitting the rate encoded signals to a centraloffice includes streaming the rate encoded signals over an IP network.12. The method of claim 11 wherein the step of streaming includesmulticasting the rate encoded signals for each channel to a plurality ofcentral offices.
 13. The method of claim 12 wherein the step ofstreaming includes streaming includes streaming the rate encoded signalson a different IP multicast address.
 14. A method for deliveringtelevision programming to a subscriber comprising: Receiving one or morechannels of program content, each channel encoded at a plurality ofdifferent rates thereby providing multiple rate encoded signals;Determining an available bandwidth of a downstream link to a subscriber;Determining a current bit rate available for transmission to thesubscriber; Selecting a best available bit rate from the multiple rateencoded signals for a requested channel; and Transmiting the selectedrate encoded signal to the subscriber.
 15. The method of claim 14wherein the step of determining a current bit rate available fortransmission to the subscriber includes: determining one or moreadditional signals that are to be transmitted to the subscriber;determining a combination of best available rate encoded signals for theone or more additional signals and the requested channel; and combiningthe best available rate encoded signals in a stream for output to thesubscriber.
 16. The method of claim 14 further comprising receiving achannel selection from the subscriber.
 17. The method of claim 16further comprising receiving a plurality of channel selections from thesubscriber including the requested channel and the one or moreadditional channels.
 18. An apparatus comprising: a termination deviceincluding an input interface for receiving one or more channels ofprogram content, each channel encoded at a plurality of different ratesthereby providing multiple rate encoded signals; a buffer to buffer themultiple rate encoded signals; a bite rate engine operable to determinean available bandwidth of a downstream link to a subscriber, determine acurrent bit rate available for transmission to the subscriber, andselect a best available bit rate from the multiple rate encoded signalsfor a requested channel; a multiplexer operable to combine selectedsignals for the subscriber; and an output interface for transmitting thecombined signal to the subscriber.
 19. The apparatus of claim 18 furtherincluding a rule set including priority rules for use in determining abest available bit rate from the multiple bit rate encoded signals. 20.The apparatus of claim 18 further including a user bit rate usagedatabase including data indicating a current bit available fortransmission to the subscriber.